This proposal focuses on the pharmacologic, physiologic, and molecular properties of the voltage-sensitive sodium channels responsible for action potential generation in neurons in the central nervous system. Excitable membrane reactions will be isolated from neuronal cell bodies, axons, and nerve terminals by subcellular fractionation techniques. The properties of sodium channels in these membrane fractions will be studied using specific neurotoxins as molecular probes. The voltage-dependent properties of the sodium channels will be examined by measuring voltage-dependent scorpion toxin binding. The effect of neurohormones, neurotransmitters, and neuromodulators on sodium channels in these different subcellular fractions will be assessed. Modulation of sodium channel properties by divalent cations and cyclic nucleotides will be examined. The effects of centrally active drugs will be studied with particular emphasis on the antiepileptic drugs and on the opiates and peptides, since physiological studies have implicated changes in sodium permeabiliity in the action of these agents. These studies will provide important new information concerning the regulation and mechanism of action of sodium channels in central neurons. Neurotoxin binding components associated with voltage-sensitive sodium channels will be solubilized from neuronal membranes and purified by conventional and affinity chromatographic techniques. The subunit composition and physical properties of these receptor sites will be determined and the physologic role of each toxin binding component in the function of the sodium channel will be assessed. Functional sodium channels will be reconstituted from purified components and the mechanisms underlying the voltage-sensitivity and ion transport activity of the sodium channel will be studied. These experiments will greatly enhance knoledge of the basic molecular mechanisms responsible for electrical excitability.